<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>首页</title>
</head>
<body>
    你好！
    {% if user_name %}
        {{ user_id }} , {{ user_name }}
    {% endif %}
</body>
</html>